EVALUATION OF FLEXURAL DEFORMATION OF A SUPER HIGH-RISE RC BUILDING BASED ON STRONG MOTION AND MICROTREMOR RECORDS AND SEISMIC RESPONSE ANALYSIS OF A THREE-DIMENSIONAL FRAME MODEL

Abstract

In last few decades, numerous super high-rise RC buildings have been constructed in Japan. During some massive earthquakes, for example, the 2011 Tohoku Earthquake (Mw 9.0), the structural response characteristics of long-period buildings were affected by excessive shaking. In super high-rise buildings, flexural deformation induced by overturning moment significantly affects the lateral displacement, especially in the upper stories. Furthermore, flexural deformation is critical for evaluating the response including higher vibrational modes excited by pulse-like ground motion and grasping the performance of seismic damping devices placed between stories. However, the flexural deformation of super high-rise buildings is insufficiently validated, because there are a few strong motion records related to flexural deformation requiring vertical observation at plural corners in the same floor.

This study examines the dynamic behavior of a super high-rise RC building focusing on flexural deformation based on strong motion and microtremor records and seismic response analysis of a three-dimensional frame model. The building is a 22-story moment-resisting RC frame structure constructed in 1995 in Saitama Prefecture, Japan. Strong motion is observed at four points inside the building; three are at the corners of the building’s rooftop and one on the first floor.

First, using strong motion data, the flexural and shear deformation variations with nonlinear behavior of the building before and after the 2011 Tohoku Earthquake were investigated. The amplitude dependence related with decrease of natural frequency and increase of damping factor was made clear. Moreover, the decrease in normalized top rotational angle in the total deformation was also confirmed from the eigenmodes at the top of the building using the system identification based on the subspace method.

Second, simulation analyses of the strong motion records are performed using a three-dimensional frame model consisting of a superstructure and rocking spring at the base. The model is validated by comparing the simulated horizontal and rotational responses with the observed records at the top of the building during a small earthquake and the 2011 Tohoku Earthquake. The relationships between maximum response values, story shear forces, and inter-story displacements obtained from the pushover analysis confirmed the decrease in the inter-story flexural deformation rate because of the nonlinearity of the shear component during the 2011 Tohoku Earthquake. Obtained results are consistent with the decrease in the flexural deformation inferred from the strong motion records.

Finally, the detailed distribution of vertical displacement regarding the flexural deformation is investigated by microtremor measurements including plural points at the rooftop. The distribution of vertical displacement at the top of the frame along the building perimeter is different from those along the center line with a central void, which is also indicated by the simulated results using the three-dimensional frame model.